This invention relates to current sources for transistor circuits and more particularly to a temperature compensated transistor current source that is suitable for manufacture in integrated circuit form.
Integrated current sources such as are described in chapter 4 of Analysis and Design of Analog Integrated Circuits by P. R. Gray and R. G. Meyer, John Wiley & Sons, 1977; section four of the booklet 101 Analog Integrated Circuit Designs by Interdesign; Inc., Sunnyvale, Calif., 1976; and U.S. Pat. No. 3,700,929, Oct. 24, 1972, Integrated Bi-Stable Circuit by T. M. Fredriksen, have been used in analog integrated circuits to make them less sensitive to power supply and temperature variations. In addition, improved temperature stability is provided by using a Zener diode to set a reference voltage in the current source. Although such a source is somewhat temperature compensated, it requires a supply voltage that must of necessity be greater than the Zener voltage, which may be greater than 7 volts. Temperature compensated integrated circuits are also described in U.S. Pat. Nos. 3,703,650, Nov. 21, 1972, by L. J. Kendall and 3,703,651, Nov. 21, 1972 by W. L. Blowers.
An object of this invention is the provision of an improved temperature compensated current source which is suitable for manufacture in integrated circuit form and which may operate from a supply voltage that is less than such a Zener voltage.